1. Field of the Invention
This invention relates to urethane modified water dispersible epoxy resin systems and their method of preparation.
2. Description of the Prior Art
In the prior art, the problems of viscosity control and gelation during the processing of waterborne epoxy amine adducts are often discussed. For instance, U.S. Pat. No. 4,608,405 to DeGooyer discloses the use of large excesses of amine which must later be vacuum stripped from the product (column 5, lines 15-33). U.S. Pat. No. 5,089,100 to Debroy discloses the partial defunctionalization of the epoxy with a secondary monoamine prior to the polyamine reaction in order to prevent gelation (column 3, lines 48-50). U.S. Pat. No. 5,096,556 to Corrigan discloses the use of blocked polyamines (ketimines) and the use of excess amine to minimize the danger of gelation (column 3, lines 64-68 and column 4, lines 48-53).
U.S. Pat. No. 5,204,385 to Naderhoff discloses the preparation and use of amine functional curing agents that are suitable for crosslinking epoxy resins in waterborne systems.
Although waterborne epoxy systems have been in commercial use for nearly 20 years, disadvantages such as slow cure rate, short pot life, and poor chemical resistance have limited their widespread acceptance.
It is an objective of the present invention to provide improvements in cure speed, adhesion, and chemical resistance in waterborne dispersions, and to provide an improved process for preparing waterborne dispersions.